Speaking at the Portsmouth Naval Shipyard, Biden said the Islamic State militant group responsible for beheading James Foley and Steven Sotloff won't intimidate the United States.

"The American people are so much stronger, so much more resolved than any enemy can fully understand," Biden said. "As a nation, we're united. And when people harm Americans, we don't retreat, we don't forget."

A videotape showing Sotloff's murder was broadcast Tuesday, two weeks after the same group released a video showing Foley's killing. Foley was from New Hampshire and Sotloff attended school there, bringing their killings close to home for many in attendance. The shipyard employs many New Hampshire residents.

"We take care of those who are grieving and when that's finished, they should know we will follow them to the gates of hell until they are brought to justice," Biden said. "Because hell is where they'll reside."

Biden's used "gates of hell" before, invoking it in an October 2012 vice presidential debate when talking about the killing of Osama bin Laden.

After the shipyard visit, he made an unannounced visit to the Old Ferry Landing restaurant in nearby Portsmouth, New Hampshire, startling lunchgoers, who broke into cheers. He snagged a young woman's cellphone and took a picture with her, then kissed a baby.

Joining Biden at the shipyard on an island in the river that separates Maine and New Hampshire were Sen. Jeanne Shaheen and Rep. Carol Shea-Porter of New Hampshire, along with Reps. Chellie Pingree and Mike Michaud of Maine. Shaheen, Shea-Porter and Pingree are up for re-election. Michaud is running for governor in Maine.

Biden is a potential 2016 Democratic candidate for president and trips to the shipyard have become a popular stop for those seeking their party's nomination.

The 214-year-old Navy yard that repairs and overhauls nuclear submarines in Kittery, Maine, has survived three reviews from the Base Closure and Realignment Commission, including the most recent in 2005. The Defense Department has pressed for another round but has been rebuffed by Congress.

Shaheen said the congressional delegation will stand in the way of any further attempts to shut down the facility, which employs about 6,000 people and which she described as an economic engine for Maine and New Hampshire.